1 | /* SPDX-License-Identifier: GPL-2.0 */ |
2 | /* rwsem.h: R/W semaphores, public interface |
3 | * |
4 | * Written by David Howells (dhowells@redhat.com). |
5 | * Derived from asm-i386/semaphore.h |
6 | */ |
7 | |
8 | #ifndef _LINUX_RWSEM_H |
9 | #define _LINUX_RWSEM_H |
10 | |
11 | #include <linux/linkage.h> |
12 | |
13 | #include <linux/types.h> |
14 | #include <linux/kernel.h> |
15 | #include <linux/list.h> |
16 | #include <linux/spinlock.h> |
17 | #include <linux/atomic.h> |
18 | #include <linux/err.h> |
19 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
20 | #include <linux/osq_lock.h> |
21 | #endif |
22 | |
23 | struct rw_semaphore; |
24 | |
25 | #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK |
26 | #include <linux/rwsem-spinlock.h> /* use a generic implementation */ |
27 | #define __RWSEM_INIT_COUNT(name) .count = RWSEM_UNLOCKED_VALUE |
28 | #else |
29 | /* All arch specific implementations share the same struct */ |
30 | struct rw_semaphore { |
31 | atomic_long_t count; |
32 | struct list_head wait_list; |
33 | raw_spinlock_t wait_lock; |
34 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
35 | struct optimistic_spin_queue osq; /* spinner MCS lock */ |
36 | /* |
37 | * Write owner. Used as a speculative check to see |
38 | * if the owner is running on the cpu. |
39 | */ |
40 | struct task_struct *owner; |
41 | #endif |
42 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
43 | struct lockdep_map dep_map; |
44 | #endif |
45 | }; |
46 | |
47 | /* |
48 | * Setting bit 1 of the owner field but not bit 0 will indicate |
49 | * that the rwsem is writer-owned with an unknown owner. |
50 | */ |
51 | #define RWSEM_OWNER_UNKNOWN ((struct task_struct *)-2L) |
52 | |
53 | extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem); |
54 | extern struct rw_semaphore *rwsem_down_read_failed_killable(struct rw_semaphore *sem); |
55 | extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem); |
56 | extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem); |
57 | extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *); |
58 | extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem); |
59 | |
60 | /* Include the arch specific part */ |
61 | #include <asm/rwsem.h> |
62 | |
63 | /* In all implementations count != 0 means locked */ |
64 | static inline int rwsem_is_locked(struct rw_semaphore *sem) |
65 | { |
66 | return atomic_long_read(&sem->count) != 0; |
67 | } |
68 | |
69 | #define __RWSEM_INIT_COUNT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE) |
70 | #endif |
71 | |
72 | /* Common initializer macros and functions */ |
73 | |
74 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
75 | # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname } |
76 | #else |
77 | # define __RWSEM_DEP_MAP_INIT(lockname) |
78 | #endif |
79 | |
80 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
81 | #define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL |
82 | #else |
83 | #define __RWSEM_OPT_INIT(lockname) |
84 | #endif |
85 | |
86 | #define __RWSEM_INITIALIZER(name) \ |
87 | { __RWSEM_INIT_COUNT(name), \ |
88 | .wait_list = LIST_HEAD_INIT((name).wait_list), \ |
89 | .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \ |
90 | __RWSEM_OPT_INIT(name) \ |
91 | __RWSEM_DEP_MAP_INIT(name) } |
92 | |
93 | #define DECLARE_RWSEM(name) \ |
94 | struct rw_semaphore name = __RWSEM_INITIALIZER(name) |
95 | |
96 | extern void __init_rwsem(struct rw_semaphore *sem, const char *name, |
97 | struct lock_class_key *key); |
98 | |
99 | #define init_rwsem(sem) \ |
100 | do { \ |
101 | static struct lock_class_key __key; \ |
102 | \ |
103 | __init_rwsem((sem), #sem, &__key); \ |
104 | } while (0) |
105 | |
106 | /* |
107 | * This is the same regardless of which rwsem implementation that is being used. |
108 | * It is just a heuristic meant to be called by somebody alreadying holding the |
109 | * rwsem to see if somebody from an incompatible type is wanting access to the |
110 | * lock. |
111 | */ |
112 | static inline int rwsem_is_contended(struct rw_semaphore *sem) |
113 | { |
114 | return !list_empty(&sem->wait_list); |
115 | } |
116 | |
117 | /* |
118 | * lock for reading |
119 | */ |
120 | extern void down_read(struct rw_semaphore *sem); |
121 | extern int __must_check down_read_killable(struct rw_semaphore *sem); |
122 | |
123 | /* |
124 | * trylock for reading -- returns 1 if successful, 0 if contention |
125 | */ |
126 | extern int down_read_trylock(struct rw_semaphore *sem); |
127 | |
128 | /* |
129 | * lock for writing |
130 | */ |
131 | extern void down_write(struct rw_semaphore *sem); |
132 | extern int __must_check down_write_killable(struct rw_semaphore *sem); |
133 | |
134 | /* |
135 | * trylock for writing -- returns 1 if successful, 0 if contention |
136 | */ |
137 | extern int down_write_trylock(struct rw_semaphore *sem); |
138 | |
139 | /* |
140 | * release a read lock |
141 | */ |
142 | extern void up_read(struct rw_semaphore *sem); |
143 | |
144 | /* |
145 | * release a write lock |
146 | */ |
147 | extern void up_write(struct rw_semaphore *sem); |
148 | |
149 | /* |
150 | * downgrade write lock to read lock |
151 | */ |
152 | extern void downgrade_write(struct rw_semaphore *sem); |
153 | |
154 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
155 | /* |
156 | * nested locking. NOTE: rwsems are not allowed to recurse |
157 | * (which occurs if the same task tries to acquire the same |
158 | * lock instance multiple times), but multiple locks of the |
159 | * same lock class might be taken, if the order of the locks |
160 | * is always the same. This ordering rule can be expressed |
161 | * to lockdep via the _nested() APIs, but enumerating the |
162 | * subclasses that are used. (If the nesting relationship is |
163 | * static then another method for expressing nested locking is |
164 | * the explicit definition of lock class keys and the use of |
165 | * lockdep_set_class() at lock initialization time. |
166 | * See Documentation/locking/lockdep-design.txt for more details.) |
167 | */ |
168 | extern void down_read_nested(struct rw_semaphore *sem, int subclass); |
169 | extern void down_write_nested(struct rw_semaphore *sem, int subclass); |
170 | extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass); |
171 | extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock); |
172 | |
173 | # define down_write_nest_lock(sem, nest_lock) \ |
174 | do { \ |
175 | typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \ |
176 | _down_write_nest_lock(sem, &(nest_lock)->dep_map); \ |
177 | } while (0); |
178 | |
179 | /* |
180 | * Take/release a lock when not the owner will release it. |
181 | * |
182 | * [ This API should be avoided as much as possible - the |
183 | * proper abstraction for this case is completions. ] |
184 | */ |
185 | extern void down_read_non_owner(struct rw_semaphore *sem); |
186 | extern void up_read_non_owner(struct rw_semaphore *sem); |
187 | #else |
188 | # define down_read_nested(sem, subclass) down_read(sem) |
189 | # define down_write_nest_lock(sem, nest_lock) down_write(sem) |
190 | # define down_write_nested(sem, subclass) down_write(sem) |
191 | # define down_write_killable_nested(sem, subclass) down_write_killable(sem) |
192 | # define down_read_non_owner(sem) down_read(sem) |
193 | # define up_read_non_owner(sem) up_read(sem) |
194 | #endif |
195 | |
196 | #endif /* _LINUX_RWSEM_H */ |
197 | |